Field of the Invention
This invention relates to a turbocharger for an internal combustion engine. More particularly, this invention relates to turbocharger having an elliptical diffuser.
Description of Related Art
A turbocharger is a type of forced induction system used with internal combustion engines. Turbochargers deliver compressed air to an engine intake, allowing more fuel to be combusted, thus boosting an engine's horsepower without significantly increasing engine weight. Thus, turbochargers permit the use of smaller engines that develop the same amount of horsepower as larger, normally aspirated engines. Using a smaller engine in a vehicle has the desired effect of decreasing the mass of the vehicle, increasing performance, and enhancing fuel economy. Moreover, the use of turbochargers permits more complete combustion of the fuel delivered to the engine, which contributes to the highly desirable goal of a cleaner environment.
Turbochargers typically include a turbine housing connected to the engine's exhaust manifold, a compressor housing connected to the engine's intake manifold, and a center bearing housing coupling the turbine and compressor housings together. A turbine wheel in the turbine housing is rotatably driven by an inflow of exhaust gas supplied from the exhaust manifold. A shaft rotatably supported in the center bearing housing connects the turbine wheel to a compressor impeller in the compressor housing so that rotation of the turbine wheel causes rotation of the compressor impeller. The shaft connecting the turbine wheel and the compressor impeller defines an axis of rotation. As the compressor impeller rotates, it increases the air mass flow rate, airflow density and air pressure delivered to the engine's cylinders via the engine's intake manifold.
The turbine wheel of a turbocharger rotates very fast. The rotation speed of a turbine wheel is size dependent, and smaller turbine wheels can rotate faster than larger wheels. A turbocharger turbine wheel used in conjunction with an internal combustion engine may reach circumferential tip speeds of 530 meters per second. The rapid rotation of the turbine wheel is directly transmitted to the compressor wheel which likewise rotates extremely rapidly. Accordingly, the gas coming off the compressor wheel is moving at a high velocity.
After being accelerated by the compressor wheel, the air proceeds into the diffuser and into the volute housing, before being exhausted at the compressor exit. The diffuser slows down the high-velocity air, largely without losses, so that both pressure and temperature rise. The diffuser accomplishes this increase by essentially forcing the air from the compressor wheel to pass through a narrow passage way. The high velocity air can't get through the narrow channel at low pressure. Thus, the pressure and temperature of the air increases. The diffuser may also have various constrictions or pinches to provide further constriction. The diffuser may have a front pinch, a rear pinch or even a double pinch. Commonly, one wall of the diffuser is formed by the compressor cover face. The other wall is formed by the wall of the compressor housing.
US 2012/0269659 relates to an exhaust-gas turbocharger having a turbine, and having a compressor which has a compressor housing, the compressor housing being fastened to a bearing housing and having a compressor spiral and a bearing-housing-side diffuser wall, wherein the compressor housing is formed as a pressure-die-cast housing, and the diffuser wall is formed as a separate component which can be connected to the compressor housing and which has an internal rounding in the transition region to the inner wall of the compressor housing spiral.
US 2010/0202877 relates to a housing for a turbocharger. The housing has an impeller chamber, diffuser and scroll in fluid communication with each other. The diffuser can have a curved shape and/or a bend in proximity to a tip of the impeller. The curved shape can be defined by one or more radii of curvature. The diffuser can extend in a radial direction that is non-orthogonal to the center line of the turbocharger. The housing can be for a compressor section of the turbocharger.
US 2008/0267765 and U.S. Pat. No. 8,287,233 relate to a centrifugal compressor with a re-circulation venture in ported shroud. An exemplary port includes a first port opening positioned at a location downstream from a compressor wheel, a second port opening positioned at a location adjacent to a blade of the compressor wheel, and a third port opening positioned at a location upstream from the compressor wheel wherein the first port opening and the third port opening define a first flow path and wherein a second flow path extending from the second port opening meets the first flow path at a confluence. The first flow path optionally includes a venturi section, for example, wherein the confluence coincides at least in part with the venturi section. Other exemplary ports, compressor shrouds, systems and methods are also disclosed.